In the discussion of the background that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
Kaolin is a naturally-occurring hydrated aluminum silicate crystalline mineral (kaolinite), in the form of hexagonally shaped, stacked platelets of irregular orientation. Hydrous kaolin is characterized by its fine particle size, plate like or lamellar particle shape, and chemical inertness.
Current methods of producing calcined kaolin involve preparing a chemically dispersed blunged/degritted kaolin crude, subjecting it to centrifugation and magnetic separation, followed by spray drying, pulverization, calcination and pulverization. Current techniques for obtaining finer particle size kaolin, such as media grinding, have a detrimental effect on the morphology of the calcined kaolin and a negative impact on performance in the final application of the kaolin product.
Calcination of kaolin at temperatures up to about 1100° C. cements particles together and produces products of improved whiteness and opacity. Such pigments are widely used by the paper, plastics, rubber and paint industries. U.S. Pat. No. 3,586,523 to Fanselow et al, is directed to producing low abrasion fine particle size opacifying calcined kaolin clay, such as the pigments supplied under the registered trademarks ANSILEX® and ANSILEX® 93. Such pigments have an average particle size of about 0.8 microns.
There is an on-going unmet need in the art for a heat-treated kaolin product with both a finer and steeper particle size distribution and useful performance properties and methods of producing same in order to improve performance in various applications. The present disclosure addresses this need.